# Atbash Cipher

Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.

The Atbash cipher is a simple substitution cipher that relies on
transposing all the letters in the alphabet such that the resulting
alphabet is backwards. The first letter is replaced with the last
letter, the second with the second-last, and so on.

An Atbash cipher for the Latin alphabet would be as follows:

```plain
Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: zyxwvutsrqponmlkjihgfedcba
```

It is a very weak cipher because it only has one possible key, and it is
a simple monoalphabetic substitution cipher. However, this may not have
been an issue in the cipher's time.

Ciphertext is written out in groups of fixed length, the traditional group size
being 5 letters, and punctuation is excluded. This is to make it harder to guess
things based on word boundaries.

## Examples
- Encoding `test` gives `gvhg`
- Decoding `gvhg` gives `test`
- Decoding `gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt` gives `thequickbrownfoxjumpsoverthelazydog`

## Setup

There are two different methods of getting set up to run the tests with Objective-C:

- Create an Xcode project with a test target which will run the tests.
- Use the ruby gem `objc` as a test runner utility.

Both are described in more detail here: http://exercism.io/languages/objective-c


### Submitting Exercises

When submitting an exercise, make sure your solution file is in the same directory as the test code.

For example, if you're submitting `Bob.m` for the Bob exercise, the submit command would be something like `exercism submit <path_to_exercism_dir>/objective-c/bob/Bob.m`.

## Source

Wikipedia [http://en.wikipedia.org/wiki/Atbash](http://en.wikipedia.org/wiki/Atbash)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.